F 

P5 


No -SL2 

Minnesota  Stale  forest  Servio 


Issued  July  27,  1912. 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

FOREST   SERVICE— Circular  201. 

HENRY  S.  GRAVES,   Forester. 


EMORY  OAK  IN  SOUTHERN  ARIZONA. 


By 


FRANK  J.  PHILLIPS, 

Collaborator. 


34820s— 12  WASHINGTON  :  GOVERNMENT  PRINTING  OFFICE  :  1912 


CONTENTS 


Page. 

Range  and  occurrence 3 

Climate " 3 

Soil  and  moisture 4 

Associated  species 4 

Characteristics  pi  the  tree 5 

Form 5 

Foliage 6 

Root  system 6 

Growth 6 

Reproduction 8 

Causes  of  injury 10 

Fire 10 

Fire  prevention 10 

Insects 11 

Wind 11 

Grazing 11 

Fungi  and  mistletoe 11 

Other  injuries 12 

Utilization 12 

Cordwood 13 

Tannin  possibilities 14 

Other  uses 14 

Management 15 


ILLUSTRATIONS. 


Page. 
Plate  I.  Fig.  1 — Typical  stand  of  veteran  Emory  oak.     Fig.  2 — Thicket  stand 

of  Emory  oak 4 

II.  Fig.  1 — Nearly  pure  thicket  stand  of  Emory  oak.     Fig.  2 — Mixed 

stand  of  Emory  oak  and  white-leaved  oak 4 

III.  Characteristic  root  collars  of  Emory  oak 8 

IV.  Leaves  of  Emory  oak  and  Arizona  white  oak 8 

V.  Fig.  1— Veteran  Emory  oak.     Fig.  2— Effect  of  pollarding  old  Emory 

oak 12 

2 


/ 


EMORY  OAK  IN  SOUTHERN  ARIZONA. 


Emory  oak  {Quercus  emoryi)  forms  one  of  the  most  important 
types  of  the  open  woodland  forest  of  the  Southwest,  and  is  the  most 
common  oak  in  the  mountains  of  southern  New  Mexico  and  Arizona. 
It  affords  protection  to  watersheds,  and  has  high  value  for  fuel  in 
a  region  where  wood  is  scarce.  Also,  there  is  a  possibility  that 
its  bark,  which  is  fairly  rich  in  tannin,  may  become  a  source  of  tannic 
acid  for  the  Southwest. 

RANGE  AND  OCCURRENCE. 

The  east  and  west  range  of  Emory  oak  is  from  western  Texas  to 
the  western  slopes  of  the  Pajarito  Mountains,  Ariz.;  from  north 
to  south  it  occurs  from  the  south-central  portion  of  Arizona  (south 
of  the  Colorado  Plateau)  to  the  south-central  part  of  the  Province 
of  Chihuahua,  Mexico.  In  Texas  it  grows  on  most  of  the  mountain 
ranges  west  of  the  Pecos  River,  and  is  especially  abundant  in  the 
canyons  and  on  the  southern  slopes  of  the  Limpio  and  Chisos  Moun- 
tains. Its  best  development  in  the  United  States  is  probably  in 
the  Garces  National  Forest,  in  southern  Arizona,  where  it  furnishes 
at  least  half  of  the  timber  supply.  Here  it  is  valued  for  fuel  more 
than  any  other  native  oak. 

CLIMATE. 

The  climate  typical  of  the  region  within  which  Emory  oak  grows 
is  that  of  the  mountains  along  the  Mexican  border,  where  the  two 
rainy  seasons  are  from  November  to  March,  inclusive,  and  from 
July  to  September.  At  the  base  of  the  foothills  the  average  annual 
precipitation  is  approximately  from  11  to  12  inches;  but  in  the 
mountains  it  may  be  as  much  as  25  inches  for  a  series  of  years,  or 
even  more  in  exceptional  years. 

The  winter  rains,  which  are  very  irregular,  originate  on  the  Pacific 
coast,  and  are  usually  preceded  by  easterly  winds.  They  are  not 
as  torrential  as  the  summer  rains,  which  originate  in  the  Tropics. 
From  these  the  precipitation  comes  mainly  during  the  afternoon  or 
evening  in    the  form   of   heavy  local   thunderstorms,  which  occur 

3 


4  EMORY   OAK   IN    SOUTHERN   ARIZONA. 

daily  for  periods  of  a  week  or  more  at  a  time,  starting  usually  about 
the  end  of  the  first  week  in  July.  While  these  storms  furnish  most 
of  the  soil  water  for  tree  growth,  the  evaporation,  at  low  altitudes, 
is  much  greater  than  the  precipitation. 

In  the  whole  region  there  is  but  little  tree  growth  in  the  winter 
rainy  season,  only  moderate  growth  in  the  spring  dry  season,  much 
growth  in  the  summer  rainy  season,  and  slight  growth  in  the  late 
dry  season. 

SOIL  AND  MOISTURE. 

Emory  oak  so  adapts  itself  to  conditions  of  soil  and  moisture 
that  it  is  able  to  grow  on  a  variety  of  sites,  though  it  does  best  in 
deep  alluvial  soils  with  abundant  water.  In  the  best  sites  in  the 
broad  valleys  the  soil  may  be  20  feet  deep  and  have  a  constant 
supply  of  underground  water  within  reach  of  the  roots.  In  the 
narrow  valleys  and  on  the  slope  bases  and  bench  lands  the  soil  may 
vary,  on  the  best  sites,  from  3  to  15  feet  in  depth,  with  moderately 
good  soil-moisture  conditions,  and,  in  the  best  situations,  some  peri- 
odic surface  flow  of  water.  On  the  slopes  the  site  has  a  very  decided 
influence  on  growth,  and  there  is  marked  advantage  to  the  trees  in 
the  deeper  soils  of  the  lower  slopes  and  in  the  greater  moisture  of 
north  and  east  slopes. 

ASSOCIATED  SPECIES. 

In  broad,  open  valleys  the  commonest  associates  of  Emory  oak 
are  mesquite  (Prosopis  juliflora  velutina),  acacia  (Acacia  greggii),  and 
desert  willow  (Chilopsis  linearis),  though  on  the  most  moist  situations 
there  will  be  ash  (Fraxinus  velutina),  sycamore  (Platanus  urrightii), 
and  willow  (Salix  taxifolia).  Although  scarcely  ever  found  in  the 
bottoms  of  the  valleys,  blue  oak  (Quercus  oblongifolia)  is  an  intimate 
associate  on  the  bases  of  the  slopes  that  border  these  valleys. 

In  the  narrow  valleys,  on  slope  bases,  and  on  benches  the  stand 
may  be  pure  or  mixed  with  any  one  or  all  of  the  following  species: 
Arizona  white  oak  (Quercus  arizonica),  white-leaf  oak  (Quercus 
hypoleuca),  Chihuahua  pine  (Pinus  cJiihuahuana) ,  and  alligator 
juniper  (Juniperus  pachyphlaa).  Even  when  all  are  present  Emory 
oak  usually  predominates. 

Since  slope  stands  are  transitional,  they  present  the  greatest 
diversity  of  associated  species.  Arizona  white  oak  and  white- 
leaved  oak  are  the  commonest  associates  on  north  and  east  slopes; 
on  south  and  west  slopes,  blue  oak,  mountain  mahogany  (Cer co- 
carpus  parvifolius) ,  cliff  rose,  manzanita  (Arbutus  xalapensis),  and 
numerous  shrubs.  At  elevations  of  from  6,000  to  7,000  feet  there 
is  a  considerable  mixture  of  Mexican  piiion  (Pinus  cembroides). 


Cir.  201,  Forest  Service,  U.  S.  Dept.  of  Agriculture. 


Plate  I. 


Fig. 


Typical  Stand  of  Veteran   Emory  Oak  in  the  Broad,  Open  Valleys; 
Alamo  Canyon,  Elevation  3,500  to  4,500  Feet. 


Fig. 


2.— Thicket  Stand  of  Emory  Oak  in  which  Side  Branches  have  been  Pruned 
to  a  Height  of  5  Feet;  near  Mowry  Mine,  Patagonia  Mountains. 


Cir.  201,  Forest  Service,  U.  S.  Dept.  of  Agriculture. 


PLATE  II. 


Fig.  1.— Nearly  Pure  Thicket  Stand  of  Emory  Oak  Transitional  Between 
Broad  Valley  and  Bench  Type,  with  Good  Slope  Stand  in  Background; 
Southwest  of  Mowry  Mine,  Patagonia  Mountains. 


Fig.  2.— Mixed  Stand  of  Emory  Oak  and  White-Leaved  Oak  on  a  North  Slope; 
near  Flux  Canyon,  Patagonia  Mountains. 


EMORY  OAK  IN   SOUTHERN   ARIZONA.  0 

CHARACTERISTICS  OF  THE  TREE. 
FORM. 

Emory  oak  varies  in  form  and  size  and  character  of  stand  more 
than  any  other  oaks  in  its  range,  according  to  its  situation;  its 
leaf  and  bark  forms,  however,  are  fairly  constant.  This  silvical 
variation  is  very  pronounced  in  the  extreme  forms,  although  the 
gradation  between  types  may  be  very  slight.  In  a  general  way 
there  are  characteristic  bottom  stands  and  slope  stands,  as  exem- 
plified in  the  Garces  National  Forest,  and  these  may  be  subdivided 
according  to  location.  For  the  bottom  stands  there  are:  (1)  Those 
of  the  broad  open  valleys  at  elevations  of  from  3,500  to  4,500  feet; 
(2)  those  in  narrower  valleys  at  from  4,500  to  5,500  feet;  and  (3) 
those  on  slope  bases  and  bench  lands  at  elevations  of  from  3,800 
to  5,500  feet.  There  are  two  subdivisions  of  the  slope  stands: 
(1)  Those  on  north  and  east  slopes  at  elevations  of  from  5,000  to 
7,000  feet  and  (2)  those  on  south  and  west  slopes  at  from  5,000 
to  7,000  feet. 

In  the  broad,  open  valleys  the  tree  reaches  its  maximum  devel- 
opment, with  breast-high  diameters  of  from  2  to  3  feet  and  a  total 
height  of  from  60  to  70  feet.  Indeed,  some  of  the  trees  in  these 
situations  are  3|  or  4  feet  in  diameter  and  80  feet  tall.1  In  these 
large  trees  the  clear  length  may  be  from  10  to  30  feet.  The  shape 
of  the  crown  varies  according  to  the  age  of  the  tree,  being  a  tall 
and  regular  oblong  in  the  younger  veterans  and  a  broad,  flat  oval  in 
the  old  ones.  One  strong  characteristic  is  the  flat  plane  in  which  the 
leaves  and  twigs  grow  on  the  branches.  This  peculiar  growth  is  not 
particularly  noticeable  in  standing  trees,  but  shows  very  plainly  in 
one  that  has  been  felled. 

In  the  narrow  valleys  the  trees  are  much  smaller,  with  a  breast-high 
diameter  of  from  6  to  8  inches  and  a  height  of  20  or  30  feet,  though 
occasionally  they  may  be  from  12  to  18  inches  in  diameter  and  as 
much  as  40  feet  high.  Here  the  clear  length  varies  from  1  to  15 
feet,  and  the  crown  is  a  narrow  oblong,  with  a  tendency,  however, 
toward  the  oval  in  the  older  trees.  Not  only  do  the  leaves  and 
twigs  grow  in  horizontal  planes,  even  more  markedly  than  in  the 
trees  of  the  broad  valleys,  but  the  branches  themselves  are  nearly 
at  right  angles  with  the  stem. 

In  the  slope  stands  the  individual  trees  are  shorter  and  have  a 
wider  crown  in  proportion  to  their  height.  The  stands  on  the  north 
and  east  slopes  are  from  two  to  three  times  as  dense  as  those  on 
south  and  west  slopes. 

1  Dr.  Edgar  Alexander  Mearns  states,  in  Bulletin  56,  U.  S.  National  Museum,  "Mammals  of  the  Mex- 
ican Boundary  of  the  United  States,"  that  he  has  seen  trees  in  the  neighborhood  of  the  Garces  National 
Forest  which  are  about  100  feet  high. 


6  EMORY   OAK   IN   SOUTHERN   ARIZONA. 

FOLIAGE. 

Although  usually  considered  an  evergreen,  like  the  live  oaks, 
there  may  be  times  during  the  year  when  Emory  oak  is  leafless. 
Old  trees  are  rarely  without  some  leaves,  but  younger  ones,  up  to 
15  or  20  feet  tall,  may  be  bare  for  two  or  three  weeks  before  the 
new  leaves  appear,  and,  in  dry  seasons,  even  for  a  month  or  two. 
During  normal  seasons  Emory  oak  leafs  in  late  April  or  early  May, 
but,  in  an  abnormally  dry  year,  may  not  leaf  until  June  or  early 
July.  There  is  a  current  opinion  that  all  the  old  leaves  are  shed 
just  before  the  new  crop  appears;  as  a  matter  of  fact  trees  begin 
to  shed  their  leaves  in  the  fall,  and  continue  to  do  so  throughout  the 
winter  and  early  spring. 

ROOT    SYSTEM. 

Just  as  the  form  of  the  tree  above  ground  is  determined  largely  by  the 
site,  so  is  the  root  system.  The  best  developed  roots  are  on  the  large 
trees  of  the  broad  valleys,  where  the  soil  is  deep,  porous,  and  moder- 
ately moist.  They  have  well-developed  tap  roots  and  numerous 
laterals  within  the  first  2  feet  beneath  the  surface.  The  laterals,  like 
the  branches  above,  spread  out  in  distinct  planes,  and  at  varying 
distances  from  the  stem,  have  sublaterals  that  go  down  at  right  angles 
from  3  to  10  feet.  The  laterals  that  are  close  to  the  surface  serve 
two  purposes:  First,  they  secure  proper  aeration  when  the  ground 
is  saturated;  and,  second,  they  are  needed  to  anchor  such  large- 
crowned  trees.  The  tree  has  an  overdeveloped,  or  hypertrophied, 
root  collar,  because  the  present  survivors  are  not  of  seedling  growth. 
Even  with  trees  of  undoubted  seedling  origin,  repeated  killing  back, 
either  by  fire,  browsing  animals,  or  frost  and  drought,  make  the  final 
trunk  the  survivor  of  many  sprouts  or  sets  of  sprouts. 

Other  marked  characteristics  of  the  root  system  are  the  intense 
red  color  of  the  inner  bark,  the  small  proportion  of  root  branching, 
except  near  the  root  tips,  and  the  strong  development  of  mycorrhiza. 

GROWTI  i . 

It  is  comparatively  easy  to  determine  the  growth  of  Emory  oak, 
because  its  annual  rings  are  more  distinct  than  those  of  other  black 
oaks  of  the  region  and  much  plainer  than  those  of  the  white  oaks. 
Generally  there  is  an  abrupt  formation  of  the  large  thick-walled 
vessels  in  spring,  though  on  poor  sites,  or  as  the  result  of  abnormal 
seasons,  the  annual  character  of  the  rings  may  not  be  readily  deter- 
mined. Sometimes,  as  in  seasons  of  more  than  one  distinct  growth 
period,  with  a  time  of  comparative  vegetative  rest  between,  there  will 
be  false  rings,  though  these  are  rare. 

Even  on  the  same  site  growth  may  vary  with  individual  trees  or 
groups  of  trees,  and  slightly  better  soil-moisture  conditions  in  iso- 


EMORY  OAK  IN   SOUTHERN   ARIZONA.  7 

lated  patches  will  enable  some  trees  to  put  on  their  leaves  in  a  dry- 
season  during  late  April  or  early  May,  while  most  of  the  trees  are  leaf- 
less until  June  or  July.  This  may  result  in  a  broad  ring  on  the  favored 
trees,  while  the  rest  of  the  stand  can  make  only  a  narrow  one. 

A  peculiar  growth  characterized  thousands  of  acres  in  the  Canelo 
Hills,  where  an  inch  of  rain  in  early  June  was  not  followed  by  any 
precipitation  for  a  month.  Emory  oak  and  Arizona  white  oak  devel- 
oped leaves,  which  were  not  more  than  from  1  to  2  cm.  (0.4  to  0.8 
inch)  long.  When  the  unusual  rainy  season  started  in  July  the  June 
leaves  failed  to  develop  further,  which  indicated  that  the  meristem 
tissue  had  lost  its  function,  though  the  leaves  seemed  normal  in  all 
other  respects.  New  leaves  of  normal  size  were  formed,  and  these, 
at  the  end  of  the  growing  season,  were  from  10  to  20  times  as  large  as 
the  leaves  formed  in  June.  Still  another  indication  of  the  adapta- 
bility of  the  species  to  changes  in  growth  conditions  is  the  appearance 
of  new  leaves  and  shoots  as  late  as  the  first  of  September. 

Sprouts  in  the  valley  stands  were  measured  for  height  and  diameter 
growth,  and  the  results  of  these  measurements  are  given  in  Table  1. 
" Injury  sprouts"  are  those  which  are  the  results  of  accidental 
harm,  such  as  would  come  through  grazing  or  Ore.  The  stump 
sprouts  are,  of  course,  those  which  spring  from  the  stump  of  a  felled 
tree. 

Table  1. — Height  and  diameter  growth  of  sprouts  in  valley  stands. 


Age. 

Height. 

Diameter, 

breast  high. 

Injury- 
sprouts. 

Stump 
sprouts. 

Injury 
sprouts. 

Stump 
sprouts. 

Years. 

5 

10 

15 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

70 

75 

80 

85 

90 

95 

100 

105 

110 

115 

120 

125 

130 

135 

140 

145 

150 

Feet. 
4.5 
8.7 
12.4 
15.7 
18.7 
21.3 
23.5 
25.5 
27.5 
29.2 
30.7 
32.2 
33.5 
34.7 
35.9 
37.1 
38.2 
39.3 
40.3 
41.9 
42.4 
43.4 
44.4 
45.3 
46.3 
47.3 
48.3 
49.3 
50.3 
51.3 

Feet. 
8.3 
14.5 
17.8 
20.1 
22.1 
23.8 

!25.4 

Inches. 

0.85 

1.70 

2.60 

3.50 

4.55 

5.65 

6.80 

7.90 

9.05 

10.20 

11.25 

12. 30 

13.30 

14.30 

15.30 

16. 20 

17.10 

17.95 

18. 80 

19.  CO 

20.35 

21.15 

21.85 

22.  CO 

23.30 

24.00 

24.75 

25.50 

2C.  30 

Inches. 
1.20 
2.95 
4.65 
6.15 
7.45 
8.65 
!9.85 

1  No  stumps  were  older  than  35  years. 


8 


EMORY   OAK   IN    SOUTHERN   ARIZONA. 


Table  1  shows  that  the  height  growth  is  slow  and  the  diameter 
growth  fairly  rapid,  and  that,  at  the  start,  the  growth  of  stump 
sprouts  is  better  than  that  of  injury  sprouts.  Yet,  at  35  years, 
the  rate  of  height  growth  of  the  injury  sprouts  is  2.2  feet  in  5  years 
as  against  only  1.6  feet  for  those  from  the  stump;  and  the  rate  of 
diameter  growth  of  injury  sprouts  for  the  same  period  is  1.15  inches 
and  only  1  inch  for  the  stump  sprouts.  This  difference  is  probably 
attributable  to  the  fact  that  the  injury  stools  are  younger,  and 
therefore  more  vigorous.  At  the  same  time  it  must  be  understood 
that  the  larger  number  of  sprouts  from  a  stump  will  more  than 
compensate  in  actual  volume  of  wood  production  for  a  greater 
growth  of  the  individual  injury  sprouts.  Moreover,  the  stump 
sprouts  tend  to  have  a  greater  clear  length  than  the  injury  sprouts. 

In  order  to  secure  an  exact  idea  of  the  effect  of  elevation  on  growth 
measurements  were  taken  at  intervals  of  100  feet  on  a  northeast 
slope,  the  summit  of  which  was  350  feet  above  the  valley,  with  an 
absolute  elevation  of  5,800  feet.  That  increase  in  elevation  results  in 
decreased  growth  is  shown  in  Table  2.  The  differences  in  growth 
may  be  ascribed  primarily  to  differences  in  soil  depth,  soil  moisture, 
and  protection  from  wind,  all  of  these  influences  being  more  favorable 
at  the  bases  of  the  slopes. 

Table  2. — Influence  of  elevation  on  height  and  diameter  growth  in  slope  stands. 


Average 

Average 

Average 

Altitude. 

Average 
age. 

Average 
height. 

diameter, 
breast 

yearly- 
height 

yearly 
diameter 

high. 

growth. 

growth. 

Feet. 

Years. 

Feet. 

Inches. 

Foot. 

Inch. 

5,550 

10.6 

8.03 

1.17 

0.758 

0.110 

5,650 

15.7 

7.70 

1.09 

.427 

.070 

5,750 

18.8 

7.05 

1.03 

.375 

.055 

REPRODUCTION. 

Although  Emory  oak  produces  seed  abundantly,  and  much  of  this 
seed  germinates  to  furnish  the  original  seedlings  from  which  subse- 
quent sprouts  develop,  reproduction  is  due  almost  entirely  to  sprout 
growth.  Coppice  growth  is  evident  everywhere,  but  even  where  this 
is  only  one  straight  stem,  as  in  the  broad  valleys,  careful  examina- 
tion will  reveal  its  sprout  origin.  In  fact,  diligent  search  for  a  dis- 
tinctly seedling  growth  failed  to  disclose  a  single  example.  While 
more  actual  seedling  reproduction  would  ensue  if  fires  and  grazing 
did  not  kill  back  the  growth,  another  reason  for  the  comparative 
lack  of  seedling  growth  is  the  destruction  of  the  acorns  themselves. 
These  usually  ripen  in  August  and  are  a  staple  article  of  food  with 
the  Indians  and  Mexicans,  who  collect  them  in  immense  quantities, 
gathering  them  from  the  ground.  In  a  good  year  one  man  can  pick 
up  50  pounds  of  acorns  in  a  day,  and  they  sell  for  not  less  than  5 


Cir.  201,  Forest  Service,  U.  S.  Dept.  of  Agriculture. 


Plate  III. 


I 


Characteristic  Root  Collars  of  Emory  Oak. 


Cir.  201,  Forest  Service,  U.  S.  Dept.  of  Agriculture. 


Plate  IV. 


Leaves  of  Emory  Oak  and  Arizona  White  Oak,  Showing  the  Relative  Size  of 
Foliage  Put  Forth  Before  and  After  a  Rainy  Season;  Collected  in  the 
Canelo  Hills  during  the  Last  week  of  September. 


EMORY   OAK   IN   SOUTHERN   ARIZONA.  y 

cents  a  pound,  even  when  the  supply  is  plentiful.  Birds,  bears,  and 
rodents  eat  the  acorns,  and  many  are  spoiled  by  insect  larvae. 

Since  most  of  the  stands  have  not  been  touched  by  the  ax,  the 
sprouts  originate  from  injury  to  seedling  growth,  the  principal 
sources  of  injury  being  lire,  grazing,  drought,  or  frost.  These  sprouts 
have  been  designated  "injury  sprouts,"  in  contrast  to  the  utiliza- 
tion or  stump  sprouts.  Fire  has  been  the  chief  source  of  injury, 
the  fires  having  been  set  in  the  interest  of  the  grazing  industry, 
and  rarely  extinguished  except  where  they  threatened  houses. 
Most  of  the  stools  represent  many  generations  of  sprouts,  and  none 
less  than  two  generations.  Since  the  damage  from  grazing  and  from 
unfavorable  climatic  conditions  is  restricted  to  seedlings  or  shoots, 
fire  and  cutting  account  for  the  origin  of  most  of  the  stands. 

Trees  have  been  cut  only  near  towns  and  mining  camps,  and  since 
the  stumps  persist  for  at  least  35  years,  the  resulting  sprouts  clearly 
show  their  origin.  Stump  sprouts,  like  injury  sprouts,  spring  from 
the  root  collar,  with  but  few  exceptions.  In  the  valleys  only  from 
1  to  6  per  cent  of  the  stump  sprouts  come  from  the  stem,  and  in  all 
cases  these  were  fewer  in  number  and  weaker  in  growth  than  those 
from  the  root  collar.  The  reason  for  this  lack  of  sprouting  above 
the  roots  is  found  in  the  dryness  of  the  climate  and  the  consequent 
slirinking  of  the  wood  away  from  the  bark,  so  that  there  is  but  slight 
chance  for  the  formation  of  a  callus.  In  the  narrow  valleys  at  higher 
elevations  there  was  a  slightly  greater  proportion  of  stem  sprouts — 
from  2  to  10  per  cent — due  largely  to  lower  stump  heights,  smaller 
diameter,  and  better  atmospheric  conditions.  But  even  in  stumps 
cut  close  to  the  ground  most  of  the  growth  comes  from  dormant  buds 
at  the  root  collar. 

Careful  counts  showed  that  there  is  little  if  any  difference  in  the 
sprouting  capacity  between  the  north  and  south  sides  of  the  stumps, 
and  the  shade  of  the  stump  evidently  has  no  protective  influence. 

Small  stumps  are  more  likely  to  produce  sprouts  and  sprouts  of 
greater  vigor  than  large  stumps. 

As  with  other  broadleaf  trees,  the  season  of  cutting  has  a  decided 
influence  on  the  sprouting  capacity  of  the  resultant  stump,  and  sum- 
mer cutting  is  most  likely  to  result  in  the  death  of  the  stump.  When 
land  is  to  be  cleared  for  cultivation  the  trees  are  cut  in  August  or  are 
girdled  then  and  cut  the  following  year.  Emory  oak  is  locally  con- 
sidered a  tree  which  it  is  hard  to  kill  simply  by  cutting.  Nevertheless, 
on  many  cut-over  slopes  in  the  Pajarito  Mountains  the  sprout  growth 
has  failed  entirely  on  areas  immediately  adjoining  thrifty  stands  of 
stump  coppice.  It  appears,  therefore,  that  the  season,  or  possibly  the 
method  of  cutting,  or  the  occurrence  of  a  severe  drought  have  caused 
the  failure.  It  seems  reasonable  that  the  best  time  for  cutting  to 
secure  coppice  growth  is  between  November  and  April. 


10  EMORY   OAK   IN   SOUTHERN   ARIZONA. 

CAUSES  OF  INJURY. 
FIRE. 

Emory  oak  constitutes  no  exception  to  the  general  truism  about 
any  tree  in  America — that  fire  is  its  greatest  enemy.  Fire  is  not  only 
a  source  of  injury  in  itself  but  is  the  antecedent  of  secondary  injury 
by  insects  or  fungi,  or  both  combined.  The  worst  fire  season  lasts 
from  February  until  the  heavy  rains  of  July,  and  the  most  severe  fires 
occur  in  May  or  June. 

In  the  open  valleys  the  thick  bark  of  the  old  trees  forms  a  sufficient 
protection  against  most  of  the  fires,  but  younger  trees,  up  to  2  or  3 
inches  in  diameter  at  the  base  are  seriously  injured,  and  smaller 
sprouts  and  young  shoots  are  killed  outright.  In  narrow  valleys  and 
on  bench  lands,  where  the  thickets  reach  a  maximum  density  and 
there  is  likely  to  be  a  good  deal  of  litter  on  the  ground,  the  fires  are 
extraordinarily  bad,  and  may  kill  as  much  as  30  per  cent  of  the  domi- 
nant stand  and  all  of  the  shoots  and  suppressed  growth.  Slope  stands 
are  damaged  in  direct  proportion  to  their  density  and  the  amount  of 
ground  cover. 

The  usual  fire  damage  on  all  growth  more  than  2  inches  in  diameter 
breast  high — below  that  diameter  the  trees  are  killed — consists  of  a 
scorched  bark  which  is  rarely  burned  through,  though  it  is  usually 
cracked  and  loosened  from  the  trunk.  This  permits  the  entrance  of 
fungi  which  cause  a  heart  rot  that  is  very  common. 

When  sprouts  are  killed  back  to  the  ground,  from  5  to  25  new 
shoots  spring  from  the  root  collar  and  make  a  height  growth  of 
from  1  to  4  feet  the  first  season.  If  the  fire  is  late  in  the  season  this 
growth  fails  to  harden  sufficiently  to  withstand  winter  conditions 
and  is  partially  killed  back.  Occasionally  some  of  the  very  tender 
shoots  are  affected  by  sun  scald. 

FIRE   PREVENTION. 

The  people  of  the  region  have  yet  to  learn  the  necessity  of  fire 
protection.  Yet  the  effect  of  prevention  of  fire  on  the  Garces  Na- 
tional Forest  can  not  fail  to  have  an  educative  value,  and  the  prac- 
tice of  allowing  fires  to  run  unchecked  will  come  to  an  end.  Fire 
fighting  is  comparatively  easy  because  of  the  open  nature  of  the 
stands,  which  makes  most  of  the  fires  merely  surface  fires,  except  in 
the  thickest  stands  or  during  severe  winds.  Where  the  grass  is 
thick,  the  most  effective  method  is  judicious  back-firing  supplemented 
by  beating  the  fires  out  with  squares  of  canvas  or  wet  gunny  sacks; 
where  the  grass  cover  is  thin  or  broken,  the  beating  alone  will  suffice. 
The  ground  is  not  rough,  it  imposes  no  difficulties  of  transportation, 
and  there  are  plenty  of  roads  and  trails,  so  that  fire  fighters  can  go 
readily  from  one  place  to  another.  The  one  difficulty  is  the  scarcity 
of  labor  available,  but  this  can  be  partly  met  by  an  adequate  system 
of  patrol  supplemented  by  the  use  of  the  telephone. 


EMORY   OAK   IN   SOUTHERN   ARIZONA.  11 

INSECTS. 

Observations  indicate  that  the  wood  and  bark  boring  insects  do 
considerable  damage.  In  certain  stands  as  much  as  95  per  cent 
show  the  borings  from  the  base  to  near  the  top  of  the  tree.  The 
openings  in  the  boles  and  branches  seem  to  give  entrance  to  wood- 
decaying  fungi. 

WIND. 

Windshake  is  prevalent,  affecting  one-eighth  of  the  trees  in  even 
the  most  sheltered  stands,  and  as  much  as  three-fourths  in  the  most 
exposed.  Combined  with  the  beetle  galleries,  the  shake  adds  greatly 
to  the  liability  to  severe  heart  rot. 

GRAZING. 

In  the  spring,  when  the  range  grasses  are  not  available,  cattle  and 
horses  browse  on  Emory  and  other  oaks,  mesquite,  acacia,  and  other 
woody  growth.  Where  this  growth  is  limited  and  there  is  much 
stock  the  young  oak  sprouts  may  suffer  considerably,  and  some  stools 
may  be  killed  outright  as  the  result  of  grazing,  though  such  severe 
injury  is  uncommon.  Indeed,  browsing  may  have  a  beneficial  effect 
as  a  form  of  pruning  early  in  the  dry  season,  and  certainly  the  ever- 
green oaks  are  an  important  asset  to  the  grazing  industry  in  helping 
to  carry  the  stock  over  to  the  rainy  season. 

FUNGI   AND   MISTLETOE.1 

The  heartwood  of  living  trees  of  the  Emory  oak  is  attacked  by  a 
number  of  species  of  fungi.  Polyporus  dryophilus  Berk,  frequently 
causes  a  brown  and  white  mottled  rot,  commonly  known  as  the  piped 
rot;  next  in  frequency  of  occurrence  is  Fomes  everhartii  (Ellis  and 
Gall.),  which  causes  a  whitish  rot  varying  to  brown  on  the  outer 
edges;  Polyporus  sulpJiureus  (Bull.)  Fr.  occurs  occasionally,  pro- 
ducing a  brown,  coarsely  checked  rot;  Polyporus  obtusus  Berk,  and 
Hydnum  erinaceus  Bull,  cause  whitish  rots  of  less  frequency. 

The  wood  of  dead  trees  and  timbers  of  oaks  of  this  species  are 
attacked  by  a  number  of  species  of  fungi,  which  as  a  rule  attack  first 
the  sapwood  and  later  may  rot  the  heartwood.  Ganoderma  cortissii 
(Berk.)  Murr.  causes  a  whitish,  stringy  rot  of  the  butts  of  dead  trees 
and  stumps;  Polyporus  gilvus  (Schw.)  Fr.  is  found  attacking  the 
sapwood  of  defective  living  trees,  as  well  as  that  of  dead  trees  and 
logs;  Polyporus  adustus  (Willd.)  Fr.,  Polystictus  versicolor  (L.)  Fr., 
Polystictus  sanguineus  (Mey.)  Fr.,  and  Stereum  spp.  are  also  common 
causes  of  decay  in  dead  oak  trees  and  timbers  of  this  species. 

Contributed  by  Dr.  George  G.  Hedgcock,  Office  of  Investigations  in  Forest  Pathology,  Bureau  of 
Plant  Industry. 


12 


EMORY   OAK   IN    SOUTHERN   ARIZONA. 


,  The  mistletoe  (Phoradendron  jlavescens  (Pursh.)  Nutt.)  frequently 
attacks  the  Emory  oak,  evidently  gaining  entrance  in  the  younger 
portions  of  the  twigs.  The  clusters  of  mistletoe  rob  the  limbs 
attacked  gf  a  portion  of  their  nutrition,  often  causing  the  outer  portion 
to  dwindle  and  die.  Severe  attacks  stunt  the  trees,  and  may  in 
extreme  cases  kill  them. 

OTHER   INJURIES. 

Occasional  terrific  hailstorms  of  a  local  character  defoliate  wiiole 
stands,  break  tender  shoots,  and  even  scar  the  branches.  A  few  trees 
are  girdled  and  killed  by  lightning. 

UTILIZATION. 

While  there  has  been  a  limited  utilization  of  Emory  oak  for  poles, 
posts,  and  mine  timbers,  it  is  used  almost  exclusively  for  fuel,  for 
which  it  is  preferred  to  the  other  woods  of  the  region.  Where  Emory 
oak  sells  at  $5  a  cord  for  domestic  firewood,  the  other  oaks  sell  at 
from  $3.50  to  $4.  At  the  mines  the  usual  price  for  Emory  oak  is 
S3,  and  there  is  not  a  ready  sale  for  the  other  oaks  at  $2.  It  is 
commonly  reputed  to  make  a  hotter  fire  and  to  leave  less  ash;  yet 
the  comparative  showing  of  Arizona  white  oak,  under  a  careful  test, 
indicates  that  there  is  no  warrant  for  the  existing  strong  prejudice 
against  it.     The  results  of  this  test  are  given  in  Table  3. 

Table  3. — Comparison  of  the  heating  values  of  Emory  oak  and  Arizona  white  oak.1 


Proportion  of 
ash. 

Heating  value 
per  pound. 

Heating  value  of  oaks  compared  with  available 
coal  and  oil  supplies  per  unit  of  weight. 

Part  of  tree. 

Emory  oak. 

Arizona  white  oak. 

Emory 
oak. 

Arizona 
white 
oak. 

Emory 
oak. 

Arizona 
white 
oak. 

Daw- 
son 
coal. 

Cerillos 
anthra- 
cite. 

Bakers- 
field 
crude 
oil. 

Daw- 
son 
coal. 

Cerillos 
anthra- 
cite. 

Bakers- 
field 

crude 
oil. 

Trunk,  average 

P.  cent. 
3.70 
12.47 
2.54 
9.13 
4.65 

P. cent. 
7.36 
3.70 
5.53 
17.38 
3.09 

PJ.W.2 

8,339 
7,497 
8,203 
7,839 
8,080 

B.t.u* 
7,499 
8,239 

7,  (120 
5,618 
8,244 

P.  cent. 
67 
60 
66 
63 
65 

P.  cent. 
63 
56 
62 
59 
61 

P.  cent. 
43 
39 
43 

41 
42 

P.  cent. 
60 
66 
61 
45 
66 

P.  cent. 
57 
62 
57 
42 
62 

P.  cent. 
39 
43 

40 

Bark 

29 

Top,  average 

43 

Determined  by  H.  S.  Betts,  Forest  Service. 


*  British  thermal  units. 


Table  3  shows  that  the  heat  value  of  an  average  sample,  including 
heartwood,  sap  wood,  and  bark,  from  a  butt  cut,  is  about  10  per 
cent  less  in  Arizona  white  oak  than  in  Emory  oak.  The  greatest 
difference  is  in  the  bark,  Emory  oak  being  28  per  cent  better  than 
the  white  oak.  Since  there  is  confusion  in  the  popular  mind  be- 
tween white  oak  and  blue  oak,  which  is  admittedly  inferior  as  a  fuel, 
this  may  be  an  explanation  of  a  part  of  the  prejudice;  but  men 


Cir.  201.  Forest  Service,  U.  S.  Dept.  of  Agriculture. 


Plate  V. 


EMORY   OAK   IN   SOUTHERN   ARIZONA. 


13 


who  have  used  the  three  species  and  who  readily  identify  them 
favor  Emory  oak,  probably  because  its  wood  is  more  sound  and  less 
subject  to  heart  rot  than  the  other  two  species. 

CORD  WOOD. 

Most  of  the  cordwood  is  cut  by  Mexicans,  who  prefer  the  ax  to 
the  saw,  as  most  woodsmen  do;  in  their  case,  however,  part  of  the 
preference  for  the  ax  is  due  to  their  inability  to  keep  a  saw  in  proper 
shape  to  do  good  work.  Before  the  establishment  of  the  National 
Forests  in  the  region  studied  it  was  their  custom  to  pollard  large 
trees,  or  those  which  they  thought  would  be  hard  to  split.  Even 
when  trees  were  felled  the  stumps  were  likely  to  be  3  feet  high. 
They  never  made  a  clean  cutting,  and  although  their  wastefulness 
may  be  condemned  as  far  as  individual  trees  are  concerned,  the 
resultant  effect  on  the  forest  has  been  better  than  that  which  would 
have  followed  indiscriminate  clean  cutting. 

The  wood  is  supposed  to  be  cut  and  stacked  into  cords;  yet  not  a 
single  full  cord  was  found  in  Nogales  or  at  any  of  the  mining  camps. 
Instead  of  4-foot  lengths,  the  sticks  were  not  more  than  3J  feet  long, 
and,  where  the  buyer  was  unsuspecting,  not  more  than  3  feet.  Every 
effort  is  made  to  make  the  stack  look  large  with  the  least  possible 
amount  of  wood.  The  branches  are  crooked,  and  the  piles  are  as 
loose  as  they  can  be  made — as  the  saying  is,  "so  you  could  throw  a 
dog  through  them  anywhere."  Under  these  conditions  the  actual 
solid  content  of  wood  is  much  short  of  what  it  should  be  and  of 
what  it  would  be  if  the  sticks  were  cut  full  length  and  were  well 
stacked.  The  usual  short  cord  contains  about  65  cubic  feet,  whereas 
a  full  cord  should  contain  about  72  cubic  feet,  or  about  10  per  cent 
more.  With  the  usual  3^-foot  stick  length,  65  cubic  feet  can  be 
used  as  a  converting  factor  for  cordwood  volume  tables. 

Table  4  gives  the  solid  cubic  contents  of  Emory  oak  trees  in  cubic 
feet  by  diameter  at  breastheight : 

Table  4. — Cubic  contents  of  Emory  oak,  of  various  diameters.1 


Diameter, 
breasthigh. 

Volume. 

Basis 
trees. 

Diameter, 
breasthigh. 

Volume. 

Basis 
trees. 

Inches. 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 

Cubic  feet. 

0.5 

.9 

1.6 

2.4 

3.4 

4.5 

6.0 

8.0 

10.4 

13.4 

17.0 

21.5 

27.0 

33.5 

Number. 

20 

35 

12 

10 

7 

9 

15 

4 

9 

7 

6 

2 

7 

4 

Inches. 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 

Total . . 

Cubic  feet. 
41.0 
49.5 
59.0 
68.7 
78.4 
89.7 
101.8 
113.8 
126.0 
140.0 
155.0 
170.0 

Number. 
4 
5 
1 
3 
1 
4 
1 
3 
2 
2 
2 
1 

176 

1  Includes  trees  over  3  inches  in  diameter  and  cordwood  sticks  down  to  1§  inches  middle  diameter. 


14 


EMORY   OAK   IN   SOUTHERN   ARIZONA. 


TANNIN   POSSIBILITIES. 

The  use  of  the  tannin  content  of  Emory  oak  has  often  been  sug- 
gested, although  the  tannin  would  be  very  dark  colored  unless 
clarified.  In  the  scarcity  of  other  tannic  agents  it  ought  to  furnish 
the  supply  for  an  industry  in  its  region.  Table  5  shows  the  quantity 
and  sources  of  the  tannin  in  the  three  most  prominent  oaks  of 
Arizona. 

Table  5. — Tannin  content  of  the  different   parts  of  Emory  oak,  Arizona  white  oak, 

and  blue  oak. 


Live  or 
dead  sec- 
tion. 

Location  of  section. 

Sample. 

Insoluble 

solids, 
reds,  etc. 

Soluble  solids. 

Species. 

Non- 
tannin. 

Tannin. 

Q.  emorvi 

Live 

Dead.... 
Live 

Dead.... 
Live 

Base  of  trunk 

Ultimate  branches. 
Twigs 

Bark  (32.5  per  cent) 
Wood  (67.5  inches). 

Per  cent. 

2.1 

.8 

1.2 

.7 

.8 

1.5 

.6 

.6 

.6 

1.2 

.8 

.9 

1.4 

.9 

1.0 

1.0 

1.1 

1.1 

.6 

3.7 

1.0 

1.2 

.9 

.8 

.8 

.5 

Per  cent. 
6.6 
4.4 
5.1 
5.7 
7.2 
5.8 
3.3 
2.5 
2.8 
4.9 
4.9 
4.9 
5.7 
7.3 
6.9 
2.7 
5.9 
5.1 
5.1 
4.0 
4.1 
4.1 
4.7 
6.1 
5.7 
5.2 

Per  cent. 
7.4 

3.1 
4.5 

Total 

3.7 

.  ...do 

2.6 

....do 

2.7 

Lower    branch    of 
12-inch  tree. 

Lower  branch 

Base  of  trunk 

Branch  5  feet  above 
ground  on  12-inch 
tree. 

Ultimate  branches. 

Lower  branch 

do 

Bark  (33.3  per  cent) 
Wood  (66.7  inches). 
Average 

2.9 
1.8 
2.2 

Bark  (28.7  percent) 
Wood  (71.3  inches). 

54 
3.4 
4.0 

Bark  (27 .8  per  cent) 
Wood  (72.2  inches). 
Average 

3.1 

1.7 
2.1 

Bark  (26  per  cent). . 
Wood  (74  inches)... 
Average 

2.6 
5.8 
5.0 

Total 

3.1 

Bark  (13.9  per  cent) 
Wood  (86.1  inches). 

3.0 
3.8 
3.7 

Q.  oblongifolia 

Bark  (27.3  per  cent) 
Wood  (72.7  inches). 
Average 

2.4 

Branch 

4.5 
3.9 

Total 

1.9 

According  to  Table  5,  Emory  oak  shows  a  fairly  rich  tannin  con- 
tent— 7.4  per  cent — in  the  bark  at  the  base  of  the  tree,  as  compared 
to  the  average  for  American  tanbarks  of  about  10  per  cent.  The 
prospects  for  the  commercial  use  of  Emory  oak  are  limited  to  the 
Southwest,  but  they  seem  so  good  there  that  its  possibilities  should 
be  thoroughly  studied. 

OTHER  USES. 

There  is  but  little  activity  in  mining  in  the  region,  but  even  in  the 
past,  when  the  mines  were  being  worked,  Emory  oak  was  rarely  used 
for  mine  timbers.  Yet  most  of  the  available  conifers  have  been  cut, 
and,  as  the  region  is  very  rich  in  minerals,  there  is  likely  to  be  a  strong 
local  demand  for  mine  timbers,  for  which  Emory  oak  will  be  used  to 
some  extent  with  other  native  oaks. 

Though  it  is  not  of  high  value  for  posts,  there  is  a  limited  use, 
in  the  absence  of  good  post  material. 


EMORY  OAK  IN   SOUTHERN  ARIZONA.  15 

MANAGEMENT. 

Two  principal  recommendations  are  at  the  basis  of  the  very  simple 
rules  necessary  to  the  proper  management  of  Emory  oak:  One  is  to 
keep  fires  out;  the  other  is  to  prohibit  cutting  from  July  to  September, 
and  especially  in  August.  The  best  results  in  securing  coppice 
growth  will  accrue  from  a  system  which  confines  cutting  to  the  period 
from  November  to  April,  inclusive. 

The  stands  of  large  trees  in  the  broad  open  valleys  are  the  hardest 
to  reproduce.  Badly  defective  trees  should  be  cut,  and  the  density 
of  the  stand  increased  by  protecting  the  shoots  from  stock.  Since 
the  range  animals  are  not  herded,  and  fences  are  out  of  the  question, 
a  trial  might  be  made  of  piling  brush  over  the  stumps  to  protect  the 
young  coppice.  This  will,  of  course,  increase  the  likelihood  of  injury 
by  fire,  but  these  stands  are  more  easily  protected  from  fire  than 
from  grazing. 

In  the  narrow  valleys  and  on  the  slopes  reproduction  is  more 
assured.  The  stools  are  smaller,  and  have  a  stronger  sprouting 
capacity  than  the  large  trees  in  the  broad  valleys.  Because  of  this 
difference  in  size,  it  is  easier  to  cut  low  stumps  in  the  small  stands. 
To  save  wood,  the  saw  should  be  used  in  felling  and  in  cutting  up  the 
timber  above  6  inches  in  diameter.  In  thicket  stands,  where  there 
are  several  sprouts  to  the  stool,  if  the  poorer  ones  are  thinned  out  it 
will  give  the  better  sprouts  the  advantage  of  increased  light. 

Clear  cutting  should  never  be  practiced,  and  the  wasteful  pollard- 
ing practiced  by  the  Mexican  woodchoppers,  bad  as  it  was,  is  prefer- 
able, as  a  sort  of  rough  selection  system,  to  a  clear  cutting,  which  tends 
to  lay  bare  a  large  area  and  render  all  the  unprotected  new  growth 
susceptible  to  all  sorts  of  injuries. 

Approved. 

James  Wilson, 

Secretary  of  Agriculture. 
Washington,  D.  C,  March  2,  1912. 

o 


